Process for improving stability



United States Patent 3,278,422 PROCESS FOR TMPRUVHNG STABILITY William R. Epperly, New Providence, and Francis S. Pramuk, Fanwood, N.J., assignors to Esso Research and Engineering Company, a corporation of Delaware No DraWin". Filed Aug. 23, 1065, Ser. No. 481,939 19 Claims. (U. 2083]l0) This case is a continuation-in-part of US. Serial No. 223,055, filed September 12, 1962, now abandoned entitled, Process for Improving Stability. The inventors are Francis S. Pramuk and William R. Epperly.

The present invention relates to the separation of aromatics and/or non-hydrocarbons from saturated hydrocarbons and/or olefins. More particularly, the present invention relates to an improved process for the separation of aromatics from gasolines, kerosenes, lube oils and most important of all the preparation of thermally stable hydrocarbons for use as jet fuels for supersonic aircraft. Naturally these thermally stable hydrocarbons may also be utilized as specialty oils such as white oils, turbine oils, spindle oils, hydraulic oils, etc. complished by removing sufficient aromatics from the oil to be treated with a type X molecular sieve so that a maximum of about 3 Wt. percent of aromatics is allowed to remain in the treated oil. This range is critical since if more than about 3 wt. percent of aromatics is allowed to remain in the product there Will not be a sufficient heat stability to warrant the representation that these are quality jet fuels and specialty oils.

Where thermal stability of fuels such as various jet fuels is a problem, the invention is particularly advantageous. Initially, because it can take aromatics out of feedstocks which will be used as jet fuels. Secondarily, because various unknown constitutents which can contribute to thermal instability are also removed.

In the operation of both internal combustion and jet engines, there is a serious problem caused by unknown materials in the fuel resulting in the formation of engine deposits. Furthermore, particularly in jet engines, a further problem arises in the plugging of fuel filters at low temperatures. Deposits also occur in the combustors of a jet engine and are very undersirable since they disrupt the desired fuel spray patterns in combustors, cause Warping of liners and thus reduce the amount of power that can be generated. Another reason jet fuels should be thermally stable is that they are circulated through a heat exchanger With the oil from the engine. If unstable constituents are present, the heat exchangers screens and nozzles in the fuel system become clogged with the polymeric material formed, thus causing a very real danger of malfunctioning of the engine.

Jet fuels for use in commercial aircraft are normally obtained by segregating selected refinery streams boiling in the naphtha and kerosene range, preferably having a substantial paraffinic content. In general, the fuels are not stable enough for use in supersonic jet aircraft because of the extremely high heat stability required. Treating employed for stabilizing fuel for less severe service has not been found satisfactory for stabilizing jet fuels. For instance, very severe acid treating has produced a thermally stable jet fuel. However, this process is extremely expensive and entails substantial product losses and other ditficulties. Thus, it is not suited for the largescale production which current demands, both military and civilian, have exerted upon the jet fuel market.

In addition, thermally stable oils for steam turbines are needed. These turbines are used to generate elec trical power and also to drive ships. Oils with good thermal stability are needed to minimize the formation of engine deposits and engine wear and to maximize useful This is ac- 3,278,422 Patented Oct. 11, 1966 "ice life of the oil for economic reasons. In addition, a high viscosity index, which is obtained by removing aromatics, is desirable for maintenance of viscosity over a range of operating temperatures.

The mere removal of aromatics is not sufficient in making these high quality products. For example, in producing jet fuel a portion of the aromatics can be removed and the resulting product is not satisfactory for supersonic aircraft in terms of thermal stability.

In a jet engine, there are typically three places where the thermal stability of a fuel is important. These are in the fuel tanks normally located in the wings, the fuel lines which are used to pass the fuel into the nozzle, and the actual nozzles themselves. The fuel lines are generally used to cool the lubrication system by means of fuel passing in heat exchange relationship through at least a portion of the lubricant.

Specifications defining the necessary levels of thermal stability of jet fuel can be determined on a laboratory scale by using the ASTM-CPR fuel coker rig. This is a device specifically designed for measuring thermal stability of a fuel. It is described in full in ASTM D-l 660. Briefly, the CFR fuel coker is an essentially scaled down version of a full-scale turbo engine fuel system which simultates the fuel oil heat exchanger and combustor nozzle of a jet engine. Fuel is pumped at predetermined rates through a hot heat exchanger tube which simulates the hot fuel line sections of the engine. The fuel then passes through a heated metal filter section which represents the nozzle area or small fuel passages in the hot section of the engine Where fuel degradation products may become trapped. The filter traps fuel degradation products formed during the test. Fuel degradation is measured by the increased pressure drop across the metal filter and by a visual rating of the varnish like deposits laid down on the hot heat exchanger tube. The greater the pressure drop the greater the deterioration in the fuel.

The conventional CFR fuel coker rig requires approximately six gallons of fuel in order to run satisfactory tests. For some experimental purposes this is a large feed requirement. Therefore, a modification of the CFR fuel coker rig was derived and was used. The modification is termed the microcoker test and requires only one liter of material to ascertain the test results. Otherwise the modified microcoker test is exactly analagous to the CFR fuel coker rig. The test results are given in terms of results at three temperatures. The first temperature corresponds to that of the fuel storage tank since in actual use the friction on the tank results in fairly high temperatures for the fuel stored in it. The second temperature corresponds to that of the fuel line heat exchange, and the third to that of the combustor nozzle of a jet engine. For Mach 3 aircraft the fuel temperature is expected to be 300 F., the exchanger temperature 500 F., and the nozzle temperature 600 F. The test pertinent to this invention, therefore, is the 300/500/600 stability test.

A tube rating of more than three is unsatisfactory. The pressure drop should be less .than 5 inches after a 300 minute test. It has been found that the mere partial removal of aromatics from the product still does not result in the obtaining of a sufficiently thermal stable oil. However, aromatic content can be used as a convenient index of the quality of the oil as long as a given type of processing, e.g. adsorption, is used. A change to a different process, e.g. extraction with solvents, changes the index because the degree of removal of other unstable compounds such as non-hydrocarbons is changed.

According to this invention, it has unexpectedly been discovered that thermally stable hydrocarbons, particularly jet fuels and specialty oils, may be prepared by treating hydrocarbon streams boiling in the range of 125 F. to 850 F., preferably 125 F. to 550 F. and most preferably 300 F. to 550 F. by contacting them with zeolitic adsorbent until no more than about 3 wt. percent aromatics are allowed to remain in the product. In addition, a very efficient separation of non-hydrocarbons is also effected with applicants invention. A type X or type Y sieve is to be utilized for the removal characterized by this invention. Generally, the sieve has an Angstrom range of 6.5 to 15 A. The 13X sieve is satisfactory and it has also unexpectedly been found that a X sieve may be even more effective. These adsorbents are described in US. Patent 2,882,244. A calcium substituted 13X sieve is a particularly good sieve for the desired separation. Other substituted type X sieves which may be utilized include strontium, barium, magnesium, iron, nickel, copper, silver, etc.

In US. Patent 3,130,007 there is described the zeolite Y type sieve. The crystals of zeolite Y are basically 3-dimensional frameworks of SiO., and A10 tetrahedrons crosslinked by the sharing of oxygen atoms. The electrovalence of each tetrahedron containing aluminum is balanced by the presence in the aluminosilicate framework of a cation such as an alkali metal ion. The void spaces in the framework are occupied by water molecules. However, it should be emphasized that the mere use of a type X or type Y sieve to separate the aromatics from the oils, e.g. jet fuels, is not sufficient. Aromatics must be removed in sufficient quantity so that no more than about 3 wt. percent of aromatics remains in the product. This range is critical and if any greater amount of aromatic is present than about 3 wt. percent in the various refined oils, the thermal stability will not be satisfactory.

The aromatic content of these oils is determined by separating a sample into a saturate fraction and an aromatic fraction using silica gel percolation. These two fractions can be analyzed more accurately for aromatics using mass spectrometry than the unseparated fraction. The aromatic content is calculated from the mass spectrometry results and the silica gel separation. Alternatively, aromatics can be measured by ultraviolet absorption. However, in order to obtain reliable analyses, the instrument must be calibrated using aromatics of the samples in question.

The process of the invention serves to remove the undesired aromatics from raw jet fuel. This markedly improves the luminometer number of the jet fuel. Aromatic removal from kerosene will improve the smoke point and provide a better lamp oil; in the same vein aromatic removal from lube oil improves the viscosity index. The aromatics which are removed from the turbine oil serves to increase thermal stability. The separation of aromatics in the gasoline boiling range will provide a high octane, aromatic fraction for use in gasoline.

By Way of definition, luminometer number is a dimensionless term which is used as a measure of flame temperature at a fixed flame radiation in the green-yellow band of the visible spectrum. The luminometer number of the fuel can be correlated with the combustion characteristics of fuels for use in jet engines and the like. It is determined by a. technique described in ASTM D-1740. While luminometer number of a jet fuel is an important criterion, the most important single criterion is that of thermal stability. It is known that other methods have been used to remove aromatics from raw jet fuel stocks such as solvent extraction using solvents like SO furfural and the like. None of these have effectively removed the unknown constituents which contribute to a fuels thermal instability.

An earlier patent, US. 3,148,136 whose inventor is R. A. Woodle did indicate that silica gel may be utilized to remove aromatics. There was no suggestion, however, of the critical range which has been discovered according to the process of this invention. There is no teaching within the reference of removing sufficient aromatics so that the product contains only a maximum of about 3 wt. percent aromatics.

The invention may be carried out in either the liquid or the vapor phase. When the liquid phase is utilized, appropriate temperatures will be in the range of 70 F.- 700 F., preferably 70 F.500 F. and most preferred 70 F.300 F. Sufficient pressure will be needed to maintain the feed in a substantially liquid condition. The pressure will vary from 0-300 p.s.i.a., preferably 15-200 p.s.i.a. and most preferred 15100 p.s.i.a. The appropriate feed rate in order to limit the aromatics in the product to a maximum of about 3 wt. percent will be 0.1 to 10 weight per weight of adsorbent per hour, i.e. w./w./hr., preferably 0.2 to 5 w./w./hr. and most preferably 0.4 to 3 W./w./hr.

The preferred operation is a vapor phase operation. In the case of vapor phase operations, the temperature in the molecular sieve separation zone should be maintained at about 400 F.800 F., preferably 500 F.775 F. and most preferably 600 F.-775 F. Pressure may vary between 1 and p.s.i.a., preferably 10 to 50 and most preferably 15 to 50 p.s.i.a. The feed rate should be 0.1 to 5, preferably 0.5 to 3 w./w./hr. The amount of feed per cycle to maintain a critical level of no more than about 3 wt. percent aromatic in the product which is obtained will vary between 0.02 and 5 weight per weight of adsorbent, i.e. w./w., preferably between 0.03 and 0.7 w./w. and most preferably 0.2 to 0.4 w./w. These feed quantities and rates include any desorbed hydrocarbon which is recycled to the adsorption step.

The resulting product which passes out of the molecular sieve separation zone will contain a maximum of about 3 Wt. percent of aromatics. Aromatics are usually present in typical feeds to the extent of at least 10% by weight. The aromatics and other undesired hydrocarbon and nonhydrocarbon materials will remain on the molecular sieve. The sieve may be discarded but it is far more realistic to use it repeatedly. Therefore, in the preferred embodiment of this invention the sieve to be used will be treated to a desorbing process. That is to say, the sieve will be desorbed with a displacing agent, although there are other substitutes such as steam, vacuum and assorted normal hydrocarbons.

The displacing agent, however, has been found to produce the most satisfactory results. It may be a polar or polarizable material having an appreciable aflinity for the sieve compared to the material desired to be desorbed and which will generally have a heat of adsorption approximately equal to the material that it is desired to desorb. Displacing agents are preferably used in the gaseous state. Displacing agents are also referred to as desorbents, displacing mediums and desorbing mediums. Suitable displacing medium for the process of this invention include CO S0 C to C alcohols such as methyl and ethyl alcohols, glycols, halogenated compounds such as methyl and ethyl chloride and methyl fluoride, nitrated compounds such as nitromethane and the like. The most effective displacing agent has the general formula:

R1 NRz a wherein R R and R are selected from the group consisting of hydrogen and C to C alkyl radicals. Ammonia is the especially preferred displacing medium with the C to C primary amines being next in order of preference to ammonia and C to C primary, secondary and tertiary amines following that.

Preferably, the desorption temperature after either the liquid phase or the vapor phase adsorption should be the same as the adsorption temperature used for vapor phase adsorption. The pressure may vary from 1 to 100 p.s.i.a., preferably 5 to 50 and most preferably 15 to 50 p.s.i.a. The rate of displacement may vary between .1 to 10 w./w./hr., preferably 1 to 8 and most preferably 1 to 5 w./w./hr. The amount of displacing agent used may vary between 0.01 and 5 w./w., preferably 0.02 to 2 and most preferably 0.02 to 1 w./w./cycle. In essence, the

process of this invention concerns the passing of 0.2 to 0.4 w./ w./ cycle of a hydrocarbon, i.e. a jet fuel or perhaps a turbine oil through a bed of molecular sieve adsorbents with a 6.5 to 15 A. pore size either a type X or type Y molecular sieve. The feedstock is passed through the bed at a rate of 0.5 to 3 w./w./hr. In this manner, the aromatic content of the product which emerges from the bed is a maximum of about 3% by weight. The aromatic usually present in the oil to be treated before contacting with the molecular sieve varies between 5 and 30 wt. percent usually at least The hydrocarbon fraction to be treated with this invention boils in the range of 125 F.-550 F. and contains, as mentioned above, 5 to 30 wt. percent of aromatics prior to treating. The contacting of the hydrocarbon fraction with the molecular sieve lasts for a period of 1 to 20 minutes, preferably 1 to minutes, but this is not critical. At the end of this time, the undesired products are desorbed from the molecular sieve bed so that the bed may be continued to be utilized. Vapor phase adsorption can take place with a displacing medium, ammonia, which is introduced with the feed at the adsorption temperature. The addition of displacing agent to the feed is not essential, but the preferred amount is 0.0001 to 3 wt. percent of feed. Pressure will be about 15 to 50 p.s.i.a. The desorption period lasts for about 1 to 15 minutes and is usually equal to the adsorption period. At the end of this time, adsorption may again commence and a product containing a maximum of 3 wt. percent of aromatics is obtained. Although not essential, it is usually desirable to recycle the first portion of the desorbed product to the adsorption step since its composition is approximately that of untreated feed.

Table I.Adsorptive treating Baton vapor phase FBP 488 Recovery 98.2

Gravity, API 44.3 Freezing point, F. -65 Color/colorhold, Saybolt 25/l6 Luminometer number 54 Heat content, B.t.u./# Sulfur, p.p.rn. 230 Mercaptan No. 0.4 Bromine No. 0.4 Thermal stability Tube AP 300/300/400 Reduction of the aromatic content of the jet fuel from 13.6 to 4.0 wt. percent resulted in a product with a tube rating of 4 and a pressure drop of 17.8, which is unsatisfactory. Reduction of the aromatic content to 2.5 wt. percent resulted in a product tube rating of 3 and a AP of 0.5 which is satisfactory.

Although the above-disclosed invention has been described with a certain degree of particularity, it will be understood that modifications and variations in the above may be carried out without departing from the spirit of the invention as hereinafter claimed.

What is claimed is:

1. The process of treating a hydrocarbon feedstock,

Rouge jet fuel- Run No. Cycles Feed 166-78 166-78 166-78 166-79 166-79 166-70 Conditions:

Total Feed Rate W./Hr./W 1 1.8 1 4. 2 3.6 2 2. 0 2 2. 0 3 2. 25 N11 Rate, W./llr./W 2. 0 2.0 2.0 2. 0 2. O 1 Adsorption Time, l\ lin 10 0 5 10 10 5 Desorption Time, Min Q. 10 0 5 10 10 6 Desorbute Recycled, Wt. percent of total dcsorbate. 50 50 59 50 None 65 Pro luct-Sievate:

Yield, Wt. percent 82. 6 91.1 83. 7 84. 8 73. 1 82.6 Aromatics, Wt. percent 4 13. 6 1. 5 8. 5 4. 0 2. 5 1.0 2. 0 Stability Test at 300/500/600:

ube 2 8 4 3 3-1 1 AP at 300 Min 0 22. 5 17.8 0.5 0. 05-0 0 InspoetionsSievate:

Sulfur, p.p.rn 230 17. 9 140 50. 9 21. l 7.0 22 Mercaptan No 0. 4 Nil Nil Nil N' Nil Nil Color/Colorhold, 25/-16 +30l+28 +30l+21 +30/+28 +30l+30 +30l+30 +30/+29 Luniiuometer No 54 81. 5 57. 75. 4 74. 6 89. 0 78. 4 Bromine Index 400 157. 3 215. 8 118. 2 158. 7 143. 4 127. 3

1 Other conditions: 600 F., 20 p.s.i.a. adsorption and desorption.

2 Other conditions: 600 F., 20 p.s.i.a. adsorption, 25 p.s.i.a. desorption. 3 Other conditions: 600 F., 20 p.s.i.a. adsoprtion, 23 p.s.i.a. desorption.

4 Aromatics analysis by Silica Gel Pere-l-Uass Spec.

5 Total Feed=fresh feed-l-recycle desorbate.

The above table, Table 1, indicates the criticality of having a maximum of about 3 wt. percent of aromatics remaining in the product after contacting the product with a type X molecular sieve in order to remove aromatics and other undesired constituents.

Table II.-Feed stock inspection Feed source: Baton Rouge So. La. Mix- Distillation, F.:

said hydrocarbon feed boiling at a temperature of at least F. and containing a substantial amount of aromatics which comprises passing said feed through a bed of zeolitic adsorbent, said adsorbent having a pore size of 6.5 to 15 A. whereby at least a portion of the said aromatics are removed by becoming adsorbed onto the molecular sieve, recovering a hydrocarbon having a maximum of 3 wt. percent aromatics whereby the said recovered hydrocarbon has increased thermal stability as compared to the feedstock prior to treatment.

2. The process of claim 1 wherein said feedstock is a lubricating oil fraction.

3. The process of claim 1 wherein said feedstock is a jet fuel.

4. A process of treating a hydrocarbon fraction, said fraction containing at least 5 wt. percent of aromatics wherein said hydrocarbon fraction is contacted with a type X zeolitic adsorbent, recovering a product having a maximum of 3 wt. percent aromatics whereby an increased thermal stability is obtained as compared with the said fraction prior to treatment.

5. The process of claim 4 wherein the said adsorbent is a 13X molecular sieve.

6. The process of claim 4 wherein said adsorbent is a 10X molecular sieve.

7. The process of claim 4 wherein said adsorbent is a type X with a divalent cation.

8. The process of claim 4 wherein said fraction is a hydrocarbon boiling in the range of 125 F. to 550 F.

9. The process of claim 4 wherein the said adsorbent is a type Y molecular sieve.

10. A process for treating a hydrocarbon fraction boiling in the range of 300 F. to 550 F. to improve its heat stability and luminometer number, said hydrocarbon containing at least 10 wt. percent of aromatics which comprises contacting said hydrocarbon with a zeolitic type X molecular sieve until a product is obtained having a maximum of 3 wt. percent of aromatics.

11. The process of claim 10 wherein said hydrocarbon is a jet fuel.

12. A process of treating a jet fuel, said jet fuel containing at least about wt. percent of aromatics, to improve its heat stability and luminometer number which comprises contacting said jet fuel with a type X zeolitic adsorbent whereby a product is obtained which contains a maximum of about 3 wt. percent of aromatics by at least a portion of the aromatics having been adsorbed onto said type X molecular sieve, desorbing said molecular sieve.

13. The process of claim 12 wherein said jet fuel is passed over said molecular sieve at a rate of 0.5 to 3 w./w./hr.

14. The process of claim 12 wherein said zeolitic adsorbent is desorbed with a displacing agent, said displacing agent having the formula:

wherein R R and R are selected from the group consisting of C to C alkyl radicals and hydrogen.

15. The process of claim 12 wherein said displacing agent is ammonia.

16. A process for treating a kerosene fraction, said kerosene fraction containing at least about 10 wt. percent of aromatics, to improve its heat stability and luminometer number which comprises contacting said hydrocarbon at a rate of 0.5 to 3 w./w./hr. with a type X zeolitic adsorbent at a temperature of 500 F. to 775 F., whereby at least a portion of said aromatics are adsorbed onto said molecular sieve, recovering a jet fuel containing a maximum of about 3 wt. percent aromatics, desorbing said molecular sieve of aromatics with a displacing agent at a temperature of 500 F. to 775 F.

17. The process of claim 16 wherein said type X zeolitic adsorbent is a 10X zeolitic adsorbent.

18. The process of claim 16 wherein said zeolitic adsorbent is a 13X zeolitic adsorbent.

19. The process of claim 16 wherein said displacing agent has the general formula:

wherein R R and R are selected from the group consisting of C to C alkyl radicals and hydrogen.

References Cited by the Examiner UNITED STATES PATENTS 2,899,379 8/1959 Wilchinsky et al 260-676 2,916,446 12/1959 Shuman 208-295 2,925,379 2/1960 Fleck et al. 260-676 2,950,336 8/1960 Kimberlin et al 260-676 3,063,934 11/1962 Epperly et al. 260-676 3,070,542 12/1962 Asher et al. 260-676 3,083,245 3/1963 Lindahl 260-676 3,098,814 7/1963 Epperly 260-674 3,148,136 9/1964 Woodle 208-69 3,182,017 5/1965 Fleck et al. 260-676 ALPHONSO D. SULLIVAN, Primary Examiner. 

1. THE PROCESS OF TREATING A HYDROCARBON FEEDSTOCK SAID HYDROCARBON FEED BOILING A TEMPERATURE OF AT LEAST 125* F. AND CONTAINING A SUBSTANTIAL AMUNT OF AROMATICS WHICH COMPRISES PASSING SAID FEED THROUGH A BED OF ZEOLITIC ADSORBENT, SAID ADSORBENT HAVING A PORE SIZE OF 6.5 TO 15 A. WHEREBY AT LEAST A PORTION OF THE SAID AROMATICS ARE REMOVED BY BECOMING ADSORBED ONTO THE MOLECULAR SIEVE, RECOVERING A HYDROCARBON HAVING A MAXIMUM OF 3 WT. PERCENT ATOMATICS WHEREBY THE SAID RECOVERED HYDROCARBON HAS INCREASED THERMAL STABILITY AS COMPOUNDED TO THE FEEDSTOCK PRIOR TO TREATMENT. 